1. Field of the Invention
This invention relates to voltage regulators, and more particularly to electronic circuits used to regulate voltages in automobiles and still more particularly to circuits for controlling function blocks in a multifunction voltage regulator used in automobiles.
2. Description of the Relevant Art
The problem addressed by this invention is encountered in harsh operating conditions for electronic systems, such as in the automobile industry where automobile engines are controlled by sophisticated process controllers. These controllers must operate in the automotive compartment and are thus exposed to wide fluctuations in temperature and voltage. In addition, automobile performance requirements have increased with tighter government emission requirements and fuel economy regulations, while customer expectations have required increased reliability. Automobile manufacturers have responded to the increasing demands by using more microcomputers and electronics and, to accomplish this response, they are requiring electronics manufacturers to provide circuits having smaller packages, higher degrees of integration, lower power consumption, and higher reliability, at a low cost.
To meet some of these demands, it is desirable to combine a 5 volt 1 milliamp standby regulator, a 12 volt 100 milliamp regulator, and a 5 volt 1.25 amp PWM current mode regulator into a single integrated circuit. However, problem in combining these functions onto one integrated circuit is that the layout of all the bias currents necessary to drive these functions becomes increasingly complicated as the number of functions increase.
FIG. 1 shows a typical prior art multifunction voltage regulator integrated circuit. In this integrated circuit, function block 1, function block 2, and function block 3 correspond to voltage regulators powered by a bias current generator 4 by way of bias currents such as IB.sub.1 through IB.sub.6. Typically, the bias current generator 4 is enabled through an enable function block 6 by either an IGN signal which is generated when an automobile is turned on, or an EN2 signal which is generated when a microprocessor is executing a power-down routine. When the bias current generator 4 is enabled, the function blocks 1, 2, and 3 convert a battery voltage Vbatt 8 and the bias currents generated by the bias current generator 4 into regulated voltage outputs, or functional signals such as generating reset signals and the like, depending upon the functions desired.
FIG. 1 shows the bias current generator 4 generating at least six bias currents IB.sub.1, IB.sub.2, IB.sub.3, IB.sub.4,IB.sub.5, and IB.sub.6, and driving at least three function blocks 1, 2, and 3. Even though FIG. 1 shows two bias currents for each function block, it is understood that more or less bias currents may be needed to drive a specific function. It is typical in the prior art for the current generator to produce eight bias currents. A limitation of this prior art circuit is that it becomes exceedingly complex to layout an integrated circuit as the number of bias currents and functions increase.